A seat slide adjuster includes a lower rail that is mounted to the floor of a vehicle, and an upper rail that is slidably provided to the lower rail and connected to a seat frame (see Patent Literatures 1 and 2). The seat slide adjuster is provided with a locking mechanism, in which a lock is unlocked to slide adjust the relative position of the upper rail with respect to the longitudinal direction of the lower rail to lock and use the upper rail at a desired position.